Identification,
Infrared Absorption 
197S
—[NOTE—Use the procedural blank, prepared as directed in the
Assay, to set the instrument.
]
Test solution—
Prepare as directed for the Assay preparation in the Assay.
Standard solution—
Prepare as directed for the Standard preparation in the Assay.
Cell size:
0.5 mm.
Assay—
[NOTE—Perform this procedure on at least 3 individual Capsules. The mean of the assay values obtained is the assay value.
] Transfer 1 Capsule to a round, narrow-mouth, screw-capped, 120-mL bottle, add about 20 mL of 6 N hydrochloric acid, and allow to stand, with frequent swirling, until the Capsule has dissolved. Add 10.0 mL of toluene, accurately measured, for each 25 mg of the labeled amount of simethicone in the Capsule, close the bottle securely with a cap having an inert liner, and shake by mechanical means for 5 minutes. Allow the phases to separate, draw off 10 mL of the upper organic (toluene) layer to a test tube containing 0.5 g of anhydrous sodium sulfate, agitate vigorously for 30 seconds, and allow the mixture to settle. If necessary, centrifuge the mixture to obtain a clear solution
(Assay preparation). Prepare a
Standard preparation by similarly treating a solution of
USP Polydimethylsiloxane RS in toluene having a known concentration of about 2.5 mg per mL. Prepare a procedural blank by similarly treating 10.0 mL of toluene. Concomitantly determine the absorbances of the solutions in 0.5-mm cells at the wavelength of maximum absorbance at about 7.9 µm, with an IR spectrophotometer, using the blank to set the instrument. Calculate the quantity, in mg, of [–(CH
3)
2SiO–]
n in the Capsule taken by the formula:
VC(AU / AS),
in which
V is the volume, in mL, of toluene taken to prepare the
Assay preparation; C is the concentration, in mg per mL, of
USP Polydimethylsiloxane RS in the Standard solution; and
AU and
AS are the absorbances of the
Assay preparation and the
Standard preparation, respectively.
